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  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * ACPI event handling for Wilco Embedded Controller
  4 *
  5 * Copyright 2019 Google LLC
  6 *
  7 * The Wilco Embedded Controller can create custom events that
  8 * are not handled as standard ACPI objects. These events can
  9 * contain information about changes in EC controlled features,
 10 * such as errors and events in the dock or display. For example,
 11 * an event is triggered if the dock is plugged into a display
 12 * incorrectly. These events are needed for telemetry and
 13 * diagnostics reasons, and for possibly alerting the user.
 14
 15 * These events are triggered by the EC with an ACPI Notify(0x90),
 16 * and then the BIOS reads the event buffer from EC RAM via an
 17 * ACPI method. When the OS receives these events via ACPI,
 18 * it passes them along to this driver. The events are put into
 19 * a queue which can be read by a userspace daemon via a char device
 20 * that implements read() and poll(). The event queue acts as a
 21 * circular buffer of size 64, so if there are no userspace consumers
 22 * the kernel will not run out of memory. The char device will appear at
 23 * /dev/wilco_event{n}, where n is some small non-negative integer,
 24 * starting from 0. Standard ACPI events such as the battery getting
 25 * plugged/unplugged can also come through this path, but they are
 26 * dealt with via other paths, and are ignored here.
 27
 28 * To test, you can tail the binary data with
 29 * $ cat /dev/wilco_event0 | hexdump -ve '1/1 "%x\n"'
 30 * and then create an event by plugging/unplugging the battery.
 31 */
 32
 33#include <linux/acpi.h>
 34#include <linux/cdev.h>
 35#include <linux/device.h>
 36#include <linux/fs.h>
 37#include <linux/idr.h>
 38#include <linux/io.h>
 39#include <linux/list.h>
 40#include <linux/module.h>
 41#include <linux/poll.h>
 42#include <linux/spinlock.h>
 43#include <linux/uaccess.h>
 44#include <linux/wait.h>
 45
 46/* ACPI Notify event code indicating event data is available. */
 47#define EC_ACPI_NOTIFY_EVENT		0x90
 48/* ACPI Method to execute to retrieve event data buffer from the EC. */
 49#define EC_ACPI_GET_EVENT		"QSET"
 50/* Maximum number of words in event data returned by the EC. */
 51#define EC_ACPI_MAX_EVENT_WORDS		6
 52#define EC_ACPI_MAX_EVENT_SIZE \
 53	(sizeof(struct ec_event) + (EC_ACPI_MAX_EVENT_WORDS) * sizeof(u16))
 54
 55/* Node will appear in /dev/EVENT_DEV_NAME */
 56#define EVENT_DEV_NAME		"wilco_event"
 57#define EVENT_CLASS_NAME	EVENT_DEV_NAME
 58#define DRV_NAME		EVENT_DEV_NAME
 59#define EVENT_DEV_NAME_FMT	(EVENT_DEV_NAME "%d")
 60static struct class event_class = {
 61	.owner	= THIS_MODULE,
 62	.name	= EVENT_CLASS_NAME,
 63};
 64
 65/* Keep track of all the device numbers used. */
 66#define EVENT_MAX_DEV 128
 67static int event_major;
 68static DEFINE_IDA(event_ida);
 69
 70/* Size of circular queue of events. */
 71#define MAX_NUM_EVENTS 64
 72
 73/**
 74 * struct ec_event - Extended event returned by the EC.
 75 * @size: Number of 16bit words in structure after the size word.
 76 * @type: Extended event type, meaningless for us.
 77 * @event: Event data words.  Max count is %EC_ACPI_MAX_EVENT_WORDS.
 78 */
 79struct ec_event {
 80	u16 size;
 81	u16 type;
 82	u16 event[];
 83} __packed;
 84
 85#define ec_event_num_words(ev) (ev->size - 1)
 86#define ec_event_size(ev) (sizeof(*ev) + (ec_event_num_words(ev) * sizeof(u16)))
 87
 88/**
 89 * struct ec_event_queue - Circular queue for events.
 90 * @capacity: Number of elements the queue can hold.
 91 * @head: Next index to write to.
 92 * @tail: Next index to read from.
 93 * @entries: Array of events.
 94 */
 95struct ec_event_queue {
 96	int capacity;
 97	int head;
 98	int tail;
 99	struct ec_event *entries[];
100};
101
102/* Maximum number of events to store in ec_event_queue */
103static int queue_size = 64;
104module_param(queue_size, int, 0644);
105
106static struct ec_event_queue *event_queue_new(int capacity)
107{
108	struct ec_event_queue *q;
109
110	q = kzalloc(struct_size(q, entries, capacity), GFP_KERNEL);
111	if (!q)
112		return NULL;
113
114	q->capacity = capacity;
115
116	return q;
117}
118
119static inline bool event_queue_empty(struct ec_event_queue *q)
120{
121	/* head==tail when both full and empty, but head==NULL when empty */
122	return q->head == q->tail && !q->entries[q->head];
123}
124
125static inline bool event_queue_full(struct ec_event_queue *q)
126{
127	/* head==tail when both full and empty, but head!=NULL when full */
128	return q->head == q->tail && q->entries[q->head];
129}
130
131static struct ec_event *event_queue_pop(struct ec_event_queue *q)
132{
133	struct ec_event *ev;
134
135	if (event_queue_empty(q))
136		return NULL;
137
138	ev = q->entries[q->tail];
139	q->entries[q->tail] = NULL;
140	q->tail = (q->tail + 1) % q->capacity;
141
142	return ev;
143}
144
145/*
146 * If full, overwrite the oldest event and return it so the caller
147 * can kfree it. If not full, return NULL.
148 */
149static struct ec_event *event_queue_push(struct ec_event_queue *q,
150					 struct ec_event *ev)
151{
152	struct ec_event *popped = NULL;
153
154	if (event_queue_full(q))
155		popped = event_queue_pop(q);
156	q->entries[q->head] = ev;
157	q->head = (q->head + 1) % q->capacity;
158
159	return popped;
160}
161
162static void event_queue_free(struct ec_event_queue *q)
163{
164	struct ec_event *event;
165
166	while ((event = event_queue_pop(q)) != NULL)
167		kfree(event);
168
169	kfree(q);
170}
171
172/**
173 * struct event_device_data - Data for a Wilco EC device that responds to ACPI.
174 * @events: Circular queue of EC events to be provided to userspace.
175 * @queue_lock: Protect the queue from simultaneous read/writes.
176 * @wq: Wait queue to notify processes when events are available or the
177 *	device has been removed.
178 * @cdev: Char dev that userspace reads() and polls() from.
179 * @dev: Device associated with the %cdev.
180 * @exist: Has the device been not been removed? Once a device has been removed,
181 *	   writes, reads, and new opens will fail.
182 * @available: Guarantee only one client can open() file and read from queue.
183 *
184 * There will be one of these structs for each ACPI device registered. This data
185 * is the queue of events received from ACPI that still need to be read from
186 * userspace, the device and char device that userspace is using, a wait queue
187 * used to notify different threads when something has changed, plus a flag
188 * on whether the ACPI device has been removed.
189 */
190struct event_device_data {
191	struct ec_event_queue *events;
192	spinlock_t queue_lock;
193	wait_queue_head_t wq;
194	struct device dev;
195	struct cdev cdev;
196	bool exist;
197	atomic_t available;
198};
199
200/**
201 * enqueue_events() - Place EC events in queue to be read by userspace.
202 * @adev: Device the events came from.
203 * @buf: Buffer of event data.
204 * @length: Length of event data buffer.
205 *
206 * %buf contains a number of ec_event's, packed one after the other.
207 * Each ec_event is of variable length. Start with the first event, copy it
208 * into a persistent ec_event, store that entry in the queue, move on
209 * to the next ec_event in buf, and repeat.
210 *
211 * Return: 0 on success or negative error code on failure.
212 */
213static int enqueue_events(struct acpi_device *adev, const u8 *buf, u32 length)
214{
215	struct event_device_data *dev_data = adev->driver_data;
216	struct ec_event *event, *queue_event, *old_event;
217	size_t num_words, event_size;
218	u32 offset = 0;
219
220	while (offset < length) {
221		event = (struct ec_event *)(buf + offset);
222
223		num_words = ec_event_num_words(event);
224		event_size = ec_event_size(event);
225		if (num_words > EC_ACPI_MAX_EVENT_WORDS) {
226			dev_err(&adev->dev, "Too many event words: %zu > %d\n",
227				num_words, EC_ACPI_MAX_EVENT_WORDS);
228			return -EOVERFLOW;
229		}
230
231		/* Ensure event does not overflow the available buffer */
232		if ((offset + event_size) > length) {
233			dev_err(&adev->dev, "Event exceeds buffer: %zu > %d\n",
234				offset + event_size, length);
235			return -EOVERFLOW;
236		}
237
238		/* Point to the next event in the buffer */
239		offset += event_size;
240
241		/* Copy event into the queue */
242		queue_event = kmemdup(event, event_size, GFP_KERNEL);
243		if (!queue_event)
244			return -ENOMEM;
245		spin_lock(&dev_data->queue_lock);
246		old_event = event_queue_push(dev_data->events, queue_event);
247		spin_unlock(&dev_data->queue_lock);
248		kfree(old_event);
249		wake_up_interruptible(&dev_data->wq);
250	}
251
252	return 0;
253}
254
255/**
256 * event_device_notify() - Callback when EC generates an event over ACPI.
257 * @adev: The device that the event is coming from.
258 * @value: Value passed to Notify() in ACPI.
259 *
260 * This function will read the events from the device and enqueue them.
261 */
262static void event_device_notify(struct acpi_device *adev, u32 value)
263{
264	struct acpi_buffer event_buffer = { ACPI_ALLOCATE_BUFFER, NULL };
265	union acpi_object *obj;
266	acpi_status status;
267
268	if (value != EC_ACPI_NOTIFY_EVENT) {
269		dev_err(&adev->dev, "Invalid event: 0x%08x\n", value);
270		return;
271	}
272
273	/* Execute ACPI method to get event data buffer. */
274	status = acpi_evaluate_object(adev->handle, EC_ACPI_GET_EVENT,
275				      NULL, &event_buffer);
276	if (ACPI_FAILURE(status)) {
277		dev_err(&adev->dev, "Error executing ACPI method %s()\n",
278			EC_ACPI_GET_EVENT);
279		return;
280	}
281
282	obj = (union acpi_object *)event_buffer.pointer;
283	if (!obj) {
284		dev_err(&adev->dev, "Nothing returned from %s()\n",
285			EC_ACPI_GET_EVENT);
286		return;
287	}
288	if (obj->type != ACPI_TYPE_BUFFER) {
289		dev_err(&adev->dev, "Invalid object returned from %s()\n",
290			EC_ACPI_GET_EVENT);
291		kfree(obj);
292		return;
293	}
294	if (obj->buffer.length < sizeof(struct ec_event)) {
295		dev_err(&adev->dev, "Invalid buffer length %d from %s()\n",
296			obj->buffer.length, EC_ACPI_GET_EVENT);
297		kfree(obj);
298		return;
299	}
300
301	enqueue_events(adev, obj->buffer.pointer, obj->buffer.length);
302	kfree(obj);
303}
304
305static int event_open(struct inode *inode, struct file *filp)
306{
307	struct event_device_data *dev_data;
308
309	dev_data = container_of(inode->i_cdev, struct event_device_data, cdev);
310	if (!dev_data->exist)
311		return -ENODEV;
312
313	if (atomic_cmpxchg(&dev_data->available, 1, 0) == 0)
314		return -EBUSY;
315
316	/* Increase refcount on device so dev_data is not freed */
317	get_device(&dev_data->dev);
318	stream_open(inode, filp);
319	filp->private_data = dev_data;
320
321	return 0;
322}
323
324static __poll_t event_poll(struct file *filp, poll_table *wait)
325{
326	struct event_device_data *dev_data = filp->private_data;
327	__poll_t mask = 0;
328
329	poll_wait(filp, &dev_data->wq, wait);
330	if (!dev_data->exist)
331		return EPOLLHUP;
332	if (!event_queue_empty(dev_data->events))
333		mask |= EPOLLIN | EPOLLRDNORM | EPOLLPRI;
334	return mask;
335}
336
337/**
338 * event_read() - Callback for passing event data to userspace via read().
339 * @filp: The file we are reading from.
340 * @buf: Pointer to userspace buffer to fill with one event.
341 * @count: Number of bytes requested. Must be at least EC_ACPI_MAX_EVENT_SIZE.
342 * @pos: File position pointer, irrelevant since we don't support seeking.
343 *
344 * Removes the first event from the queue, places it in the passed buffer.
345 *
346 * If there are no events in the the queue, then one of two things happens,
347 * depending on if the file was opened in nonblocking mode: If in nonblocking
348 * mode, then return -EAGAIN to say there's no data. If in blocking mode, then
349 * block until an event is available.
350 *
351 * Return: Number of bytes placed in buffer, negative error code on failure.
352 */
353static ssize_t event_read(struct file *filp, char __user *buf, size_t count,
354			  loff_t *pos)
355{
356	struct event_device_data *dev_data = filp->private_data;
357	struct ec_event *event;
358	ssize_t n_bytes_written = 0;
359	int err;
360
361	/* We only will give them the entire event at once */
362	if (count != 0 && count < EC_ACPI_MAX_EVENT_SIZE)
363		return -EINVAL;
364
365	spin_lock(&dev_data->queue_lock);
366	while (event_queue_empty(dev_data->events)) {
367		spin_unlock(&dev_data->queue_lock);
368		if (filp->f_flags & O_NONBLOCK)
369			return -EAGAIN;
370
371		err = wait_event_interruptible(dev_data->wq,
372					!event_queue_empty(dev_data->events) ||
373					!dev_data->exist);
374		if (err)
375			return err;
376
377		/* Device was removed as we waited? */
378		if (!dev_data->exist)
379			return -ENODEV;
380		spin_lock(&dev_data->queue_lock);
381	}
382	event = event_queue_pop(dev_data->events);
383	spin_unlock(&dev_data->queue_lock);
384	n_bytes_written = ec_event_size(event);
385	if (copy_to_user(buf, event, n_bytes_written))
386		n_bytes_written = -EFAULT;
387	kfree(event);
388
389	return n_bytes_written;
390}
391
392static int event_release(struct inode *inode, struct file *filp)
393{
394	struct event_device_data *dev_data = filp->private_data;
395
396	atomic_set(&dev_data->available, 1);
397	put_device(&dev_data->dev);
398
399	return 0;
400}
401
402static const struct file_operations event_fops = {
403	.open = event_open,
404	.poll  = event_poll,
405	.read = event_read,
406	.release = event_release,
407	.llseek = no_llseek,
408	.owner = THIS_MODULE,
409};
410
411/**
412 * free_device_data() - Callback to free the event_device_data structure.
413 * @d: The device embedded in our device data, which we have been ref counting.
414 *
415 * This is called only after event_device_remove() has been called and all
416 * userspace programs have called event_release() on all the open file
417 * descriptors.
418 */
419static void free_device_data(struct device *d)
420{
421	struct event_device_data *dev_data;
422
423	dev_data = container_of(d, struct event_device_data, dev);
424	event_queue_free(dev_data->events);
425	kfree(dev_data);
426}
427
428static void hangup_device(struct event_device_data *dev_data)
429{
430	dev_data->exist = false;
431	/* Wake up the waiting processes so they can close. */
432	wake_up_interruptible(&dev_data->wq);
433	put_device(&dev_data->dev);
434}
435
436/**
437 * event_device_add() - Callback when creating a new device.
438 * @adev: ACPI device that we will be receiving events from.
439 *
440 * This finds a free minor number for the device, allocates and initializes
441 * some device data, and creates a new device and char dev node.
442 *
443 * The device data is freed in free_device_data(), which is called when
444 * %dev_data->dev is release()ed. This happens after all references to
445 * %dev_data->dev are dropped, which happens once both event_device_remove()
446 * has been called and every open()ed file descriptor has been release()ed.
447 *
448 * Return: 0 on success, negative error code on failure.
449 */
450static int event_device_add(struct acpi_device *adev)
451{
452	struct event_device_data *dev_data;
453	int error, minor;
454
455	minor = ida_alloc_max(&event_ida, EVENT_MAX_DEV-1, GFP_KERNEL);
456	if (minor < 0) {
457		error = minor;
458		dev_err(&adev->dev, "Failed to find minor number: %d\n", error);
459		return error;
460	}
461
462	dev_data = kzalloc(sizeof(*dev_data), GFP_KERNEL);
463	if (!dev_data) {
464		error = -ENOMEM;
465		goto free_minor;
466	}
467
468	/* Initialize the device data. */
469	adev->driver_data = dev_data;
470	dev_data->events = event_queue_new(queue_size);
471	if (!dev_data->events) {
472		kfree(dev_data);
473		error = -ENOMEM;
474		goto free_minor;
475	}
476	spin_lock_init(&dev_data->queue_lock);
477	init_waitqueue_head(&dev_data->wq);
478	dev_data->exist = true;
479	atomic_set(&dev_data->available, 1);
480
481	/* Initialize the device. */
482	dev_data->dev.devt = MKDEV(event_major, minor);
483	dev_data->dev.class = &event_class;
484	dev_data->dev.release = free_device_data;
485	dev_set_name(&dev_data->dev, EVENT_DEV_NAME_FMT, minor);
486	device_initialize(&dev_data->dev);
487
488	/* Initialize the character device, and add it to userspace. */
489	cdev_init(&dev_data->cdev, &event_fops);
490	error = cdev_device_add(&dev_data->cdev, &dev_data->dev);
491	if (error)
492		goto free_dev_data;
493
494	return 0;
495
496free_dev_data:
497	hangup_device(dev_data);
498free_minor:
499	ida_simple_remove(&event_ida, minor);
500	return error;
501}
502
503static int event_device_remove(struct acpi_device *adev)
504{
505	struct event_device_data *dev_data = adev->driver_data;
506
507	cdev_device_del(&dev_data->cdev, &dev_data->dev);
508	ida_simple_remove(&event_ida, MINOR(dev_data->dev.devt));
509	hangup_device(dev_data);
510
511	return 0;
512}
513
514static const struct acpi_device_id event_acpi_ids[] = {
515	{ "GOOG000D", 0 },
516	{ }
517};
518MODULE_DEVICE_TABLE(acpi, event_acpi_ids);
519
520static struct acpi_driver event_driver = {
521	.name = DRV_NAME,
522	.class = DRV_NAME,
523	.ids = event_acpi_ids,
524	.ops = {
525		.add = event_device_add,
526		.notify = event_device_notify,
527		.remove = event_device_remove,
528	},
529	.owner = THIS_MODULE,
530};
531
532static int __init event_module_init(void)
533{
534	dev_t dev_num = 0;
535	int ret;
536
537	ret = class_register(&event_class);
538	if (ret) {
539		pr_err(DRV_NAME ": Failed registering class: %d\n", ret);
540		return ret;
541	}
542
543	/* Request device numbers, starting with minor=0. Save the major num. */
544	ret = alloc_chrdev_region(&dev_num, 0, EVENT_MAX_DEV, EVENT_DEV_NAME);
545	if (ret) {
546		pr_err(DRV_NAME ": Failed allocating dev numbers: %d\n", ret);
547		goto destroy_class;
548	}
549	event_major = MAJOR(dev_num);
550
551	ret = acpi_bus_register_driver(&event_driver);
552	if (ret < 0) {
553		pr_err(DRV_NAME ": Failed registering driver: %d\n", ret);
554		goto unregister_region;
555	}
556
557	return 0;
558
559unregister_region:
560	unregister_chrdev_region(MKDEV(event_major, 0), EVENT_MAX_DEV);
561destroy_class:
562	class_unregister(&event_class);
563	ida_destroy(&event_ida);
564	return ret;
565}
566
567static void __exit event_module_exit(void)
568{
569	acpi_bus_unregister_driver(&event_driver);
570	unregister_chrdev_region(MKDEV(event_major, 0), EVENT_MAX_DEV);
571	class_unregister(&event_class);
572	ida_destroy(&event_ida);
573}
574
575module_init(event_module_init);
576module_exit(event_module_exit);
577
578MODULE_AUTHOR("Nick Crews <ncrews@chromium.org>");
579MODULE_DESCRIPTION("Wilco EC ACPI event driver");
580MODULE_LICENSE("GPL");
581MODULE_ALIAS("platform:" DRV_NAME);